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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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In the preceding chapters the main theme has been the consideration of the characteristics of individual glaciers, with only incidental reference to relationships and to more general problems, the single exception being the discussion, in Chapter X, of the problems presented by the advancing glaciers. There are, however, some features common to many glaciers, some phenomena and problems relating to the region as a whole, and some of general interest because of application to other regions. It is the purpose of this chapter to briefly treat these phenomena and problems topically, introducing such repetition of statements previously made as is necessary for clear individual presentation. The first group of phenomena and problems relate to the characteristics of the glaciers themselves; the second to special problems clearly illustrated by certain of these glaciers; the third to resemblances between the existing glacial phenomena of Yakutat Bay and regions of former glaciation; and the fourth to the glacial history of the region.
As has been pointed out specifically in Chapter n, and as is clear from the descriptions in the succeeding chapters there are many different kinds of glaciers near Yakutat Bay, differing greatly in size, rate of flow, and a multitude of other characteristics. No matter how different they may be, however, they are all alike in one important respect, —in some portion of their course, often in the middle, and sometimes throughout, they are normal valley glaciers. But the valley glacier portions grade down-stream to termini which present great differences in characteristics; and up-stream there are also notable differences among the many glaciers of the region. These variations will be more specifically stated under four headings, the cornice glacier, the valley glacier, the through glacier, and glacier termini.
The Cornice Glader. The cornice glacier, common in glaciated mountain areas, is characteristically developed in the Yakutat Bay region in two relationships. First, where it is nourished by excess of snowfall on rock ledges or cliffs, being, therefore, due to favorable topographic inequality combined with such a climatic factor as a north exposure. This kind of shelf, or cornice glacier has conditions almost exactly similar to the normal valley glacier, of which it forms an incomplete type, with surface plan of great irregularity and some times with a short valley glacier projecting from it. Many of the glaciers of the Colorado, Montana, and Canadian Rocky Mountains are of this sort. They are often much larger in Alaska, and exist in hundreds in the mountains of the Yakutat Bay region, being larger on north than on south slopes, and in the irregular heads of valleys than in the smoothly-sculptured lower valley troughs,